A stepper (reduction projection exposure system) that is one semiconductor device fabrication apparatus is an apparatus that projects a pattern formed in a photomask, reticle, or the like onto a semiconductor wafer on which resist is applied while demagnifying the pattern by a projector lens.
Nowadays, as patterns have been manufactured with decreasing dimensions, a method of evaluating their performance by measuring or inspecting the formed pattern by a scanning electron microscope or the like is about to become the mainstream of semiconductor measurement and inspection. A scanning electron microscope is an instrument for imaging a sample by scanning an electron beam over the sample and detecting electrons released from the sample. That is, two regions emitting substantially the same amount of secondary electrons are represented by substantially the same brightness and so there is the possibility that it is difficult to discern the regions. Furthermore, if an electron microscope image is contaminated with noise, it might also be difficult to make such discernment. Especially, as patterns have been fabricated at higher levels of integration in recent years, patterns that are difficult to discern are found from time to time. Patent literatures 1 and 2 disclose techniques of discerning line patterns of a line-and-space pattern from spaces. In particular, patent literature 1 discloses a method of discriminating convex and concave portions of a line pattern made up of convex portions formed by two vertical inclined surfaces and one type of concave portion. Patent literature 2 explains a technique of judging whether a portion located between two peaks is a line pattern or a space based on a comparison of the peak widths of two adjacent profiles obtained by emitting a beam at an angle to an ideal optical axis.
Furthermore, if it is difficult to make a decision replying only on a two-dimensional image of a pattern, the type of the pattern can be identified by monitoring the three-dimensional morphology of the sample including the depth direction. Patent literature 3 discloses a method of estimating the three-dimensional morphology of a pattern as a method of observing a three-dimensional structure of the pattern by combining images observed from two different directions relative to a sample. Patent literature 4 discloses a method of measuring the dimensions of the top surface and bottom surface of a pattern separately by making a beam obliquely hit a pattern on the sample.
Non Patent literatures 1, 2, and 3 explain techniques for forming microscopic patterns in a semiconductor process by repeating exposure and etching, each twice.